If the converter does not see a significant load it turns off to conserve power.

It seems that about a year ago one here somebody came up a circuit that pulsed a load every so often to keep the powerbank "alive".

 

If the converter does not see a significant load it turns off to conserve power.

It seems that about a year ago one here somebody came up a circuit that pulsed a load every so often to keep the powerbank "alive".

That's an interesting thought, Dick.

However, this powerbank has three outputs - a USB-C and two USB-As. I wondered about the loading, so I plugged in the halogen lamp as well. It changed the frequency of the 'drop-outs' but they still happened. Then I tried my mobile phone in the USB-C socket. Same result.

Still, it would be worth trying a circuit to draw, say, 100mA every 15 seconds or so, just for maybe 100mS and see if that makes any difference!

 

As I recall something like that worked for one person. 100 ms might be too short (or maybe not -you won't know until you try) so if it doesn't work you might want to try a longer pulse while you have the setup together.

 

My experience with these powebanks is that they will shut off if the current falls below some minimum. Is that what you are seeing?

 

The capacitor across the supply has lowered the effective source impedance and allows very short current requirements to be satisfied without dropping the voltage to a level that causes a problem. Those very short current spikes are typical of switching supplies, and have caused problems for many folks . The great news is that you found a solution that works in a reasonably short time.

 

The solution turned out to be simpler than I thought! No capacitor, no Schottky diode. I just need to maintain around 20mA current and the powerbank remains active. So a 270 ohm, ¼ watt resistor across the 5V supply works fine, . I just wonder whether different makes of powerbank will have a similar requirement, or whether I will have to adjust for each one! Hey ho...

 

The solution turned out to be simpler than I thought! No capacitor, no Schottky diode. I just need to maintain around 20mA current and the powerbank remains active. So a 270 ohm, ¼ watt resistor across the 5V supply works fine, . I just wonder whether different makes of powerbank will have a similar requirement, or whether I will have to adjust for each one! Hey ho...

You've got me wondering too. I very much doubt this is addressed in any of the current USB standards.

5V x 20 ma = 100 mW. Maybe pulsing, if it works at such low currents would allow those who feel the need to squeeze more mah out of their powerbanks.

 

The solution turned out to be simpler than I thought! No capacitor, no Schottky diode. I just need to maintain around 20mA current and the powerbank remains active. So a 270 ohm, ¼ watt resistor across the 5V supply works fine, . I just wonder whether different makes of powerbank will have a similar requirement, or whether I will have to adjust for each one! Hey ho...

As I hinted in post #24.

 

Probably with no current drawn the power bank goes into some sleep or standby mode. The problem being that it is hard to tell the difference between "zero" and "nothing."

 

5V x 20 ma = 100 mW. Maybe pulsing, if it works at such low currents would allow those who feel the need to squeeze more mah out of their powerbanks.

I did try a brief experiment along these lines (manually touching the resistor briefly onto the power lines every few seconds!) but it didn't seem to work. This could be worth looking into in more detail, but I can easily spare the 20mA in this project, so I will leave that to others!

 

Final Update!

Having now tested this on three different makes of powerbank, the limits seem to be something like a 50mA pulse of 0.5s duration every 30s.

It is my intention to go well within these limits and design my circuit to implement a 100mA pulse (47 ohm resistor) of 0.5s duration every 20s. Some units seem happy to be 'kicked' by a lower current, but because I can't know what powerbank my users may employ, I'm working on the safe side!

Many thanks to all who have shown an interest in this thread. I do feel that there is a lot to be said for using one of these powerbanks as a portable source of 5 volts at currents up to a couple of Amps or more. They are eminently affordable, have very worthwhile capacity and contain all the charging and protection circuitry that one could need.

 

I applaud your conservative design approach. Thank you for sharing your results because this is bound to come up again in the future.